Spin Conservation Accounts for Aluminum Cluster Anion Reactivity Pattern with O

• Published in: Science (American Association for the Advancement of Science) Vol. 319; no. 5862; pp. 438 - 442
• Main Authors: Burgert, R, Schnöckel, H, Grubisic, A, Li, X, Stokes, S.T, Bowen, K.H, Ganteför, G.F, Kiran, B, Jena, P
• Format: Journal Article
• Language: English
• Published: American Association for the Advancement of Science 25-01-2008
• Subjects: Adducts; Aluminum; Anions; Atomic energy levels; Atoms; Electrons; Molecules; Oxygen; Reactivity; Singlet state
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1148643

The reactivity pattern of small (~10 to 20 atoms) anionic aluminum clusters with oxygen has posed a long-standing puzzle. Those clusters with an odd number of atoms tend to react much more slowly than their even-numbered counterparts. We used Fourier transform ion cyclotron resonance mass spectrometry to show that spin conservation straightforwardly accounts for this trend. The reaction rate of odd-numbered clusters increased appreciably when singlet oxygen was used in place of ground-state (triplet) oxygen. Conversely, monohydride clusters AlnH⁻, in which addition of the hydrogen atom shifts the spin state by converting formerly open-shell structures to closed-shell ones (and vice versa), exhibited an opposing trend: The odd-n hydride clusters reacted more rapidly with triplet oxygen. These findings are supported by theoretical simulations and highlight the general importance of spin selection rules in mediating cluster reactivity.